Re: query rewrite using materialized views

On Tue, 2005-01-04 at 13:26 -0600, Wager, Ryan D [NTK] wrote:
> Rod,
>   I do this, PG gets forked many times, it is tough to find the max
> number of times I can do this, but I have a Proc::Queue Manager Perl
> driver that handles all of the copy calls.  I have a quad CPU machine.
> Each COPY only hits ones CPU for like 2.1% but anything over about 5
> kicks the load avg up.

Sounds like disk IO is slowing down the copy then.

>   Ill get some explain analysis and table structures out there pronto.
>
> -----Original Message-----
> From: Rod Taylor [mailto:pg@rbt.ca]
> Sent: Tuesday, January 04, 2005 1:02 PM
> To: Wager, Ryan D [NTK]
> Cc: Postgresql Performance
> Subject: Re: [PERFORM] query rewrite using materialized views
>
> >   1)the 250 million records are currently whipped and reinserted as a
> > "daily snapshot" and the fastest way I have found "COPY" to do this
> from
> > a file is no where near fast enough to do this.  SQL*Loader from
> Oracle
> > does some things that I need, ie Direct Path to the db files access
> > (skipping the RDBMS), inherently ignoring indexing rules and saving a
> > ton of time (Dropping the index, COPY'ing 250 million records, then
> > Recreating the index just takes way too long).
>
> If you have the hardware for it, instead of doing 1 copy, do 1 copy
> command per CPU (until your IO is maxed out anyway) and divide the work
> amongst them. I can push through 100MB/sec using methods like this --
> which makes loading 100GB of data much faster.
>
> Ditto for indexes. Don't create a single index on one CPU and wait --
> send off one index creation command per CPU.
>
> >   2)Finding a way to keep this many records in a fashion that can be
> > easily queried.  I even tried breaking it up into almost 2800 separate
> > tables, basically views of the data pre-broken down, if this is a
> > working method it can be done this way, but when I tried it, VACUUM,
> and
> > the COPY's all seemed to slow down extremely.
>
> Can you send us EXPLAIN ANALYSE output for the slow selects and a little
> insight into what your doing? A basic table structure, and indexes
> involved would be handy. You may change column and table names if you
> like.
>
> > -----Original Message-----
> > From: pgsql-performance-owner@postgresql.org
> > [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of Josh
> Berkus
> > Sent: Tuesday, January 04, 2005 12:06 PM
> > To: pgsql-performance@postgresql.org
> > Cc: Yann Michel
> > Subject: Re: [PERFORM] query rewrite using materialized views
> >
> > Yann,
> >
> > > are there any plans for rewriting queries to preexisting
> materialized
> > > views?  I mean, rewrite a query (within the optimizer) to use a
> > > materialized view instead of the originating table?
> >
> > Automatically, and by default, no.   Using the RULES system?  Yes, you
> > can
> > already do this and the folks on the MattView project on pgFoundry are
>
> > working to make it easier.
> >
--